There is known a vehicle rear structure in which a stack case for housing a fuel cell is provided below a front floor and in which a sub-frame is provided in the rear of the stack case. A hydrogen tank is provided on the sub-frame, while the sub-frame and the stack case have flat facing surfaces (see, for example, Japanese Patent No. 3816418).
When subjected to an impact load, the sub-frame comes into contact with the stack case. The impact load is transmitted from the sub-frame to the stack case. The transmitted impact load is dispersed on a whole surface of the stack case and is supported by the stack case. To ensure that the impact load is dispersed on the whole surface of the stack case and is supported by the stack case, it is necessary to enhance strength and rigidity of the stack case. However, the enhanced strength and rigidity will jeopardize efforts to reduce the weight of the vehicle.
There is also known another vehicle rear structure in which a sub-frame is mounted on a rear frame from below and in which a lower frame is provided in the rear of the sub-frame. The lower frame opposes the sub-frame (see, for example, Japanese Patent No. 4559259). When the rear frame is subjected to an impact load, the lower frame comes into contact with the sub-frame. The impact load is transmitted from the lower frame to the sub-frame that supports the impact load. However, for the sub-frame to support the impact load, it is necessary to mount the lower frame on the rear frame, which also jeopardizes efforts to reduce the weight.